I tried waving with 10 different characters of mine at a person wearing Brilliant Love: be mine and was unable to get a single brilliant love: I'm yours. My wife then logged in and waved at the exact same person I was waving at and received a brilliant love: I'm yours on each character she tried. Furthermore, the player I was waving at brought in a second character of his and waved at himself on his second character and also received a brilliant love:I'm yours of their own.

It seems I am the only one who cannot get a brilliant love: I'm URS by waving.

^ Weird bug. Infinipure and all of his alts, when he waves at someone wearing the Brilliant Love: BE MINE! hat, hey does not get the Brilliant Love: IM URS! hat in return. Nothing happens for him. I watched him wave to 2 of my alts on his many alts, same result for all of his alts, but anyone else including other alts of mine, had no issues.

If you already have the gift item in your inventory or if you have it in your stash, it will not be granted.

What is the IGN of the character in question? Thanks!

I didn't have one in my inventory. I didn't have one in my stash. The only one I have is on a character i use as a catch all for items I've collected.
Every character on my account is the "character in question" ( Infinipure, Purebeak, Pureeyes, Pureears, Purehorn, Pureteeth, Puresupplies, Purecrafting, and Purestash). As I stated below, I tried all 9 of my characters on my account with no luck. I used the exact same device I regularly use to access my account to access my son's account and he was able to collect the helm. My wife used her device and her account and also was able to collect the hat. The person wearing the hat loaded a 2nd character and was able to get the hat too. The person wearing the hat even said several other people came wave at him and we're granted the hat.

I AM THE ONLY PERSON NOT ABLE TO WAVE AND COLLECT THE BRILLIANT LOVE: I'M URS! HAT...

Like I said, wouldn't be fixed before event ended.... Ohh well... Guess I wasn't meant to get the hat.

You can still get the Brilliant Love: IM URS! hat by waving at someone who is wearing the Brilliant Love: BE MINE! hat, even though the event has ended, so no worries.

I did give you 2 or 3 of the IM URS hats after you failed to get them by waving to me. Why don't you put all of the IM URS hats on your wife's or son's account and try again sometime. If you still have a problem, and since I have not seen this happen with anyone else, I'd be willing to hook you up with one for each of your alts so that the devs don't have to dig into what appears to be a 1-person issue. Let me know. Just PM me in Discord.